The present invention relates to an etching method and a plasma processing method.
As ultra high integration in semiconductor devices increasing in recent years, manufacturing superfine metal wirings that conform to rigorous design rules has become a crucial technical requirement. However, when the aluminum wirings normally utilized in the prior art, such as wirings constituted of Al or an Al alloy, are miniaturized, the level of the electrical resistance becomes significant, which readily causes a wiring delay, lowering the operating speed of the semiconductor device. As a solution, adoption of Cu having a lower electrical resistance value than Al as the wiring material has been considered in recent years. However, Cu becomes oxidized more readily than Al. Accordingly, during the semiconductor manufacturing process, a Cu wiring layer is covered with a layer constituted of a material that does not contain O2, e.g., an SiNx layer, to prevent oxidation of the Cu wiring layer by assuring that it is not exposed to O2.
When connecting a Cu wiring to another wiring in a semiconductor device adopting a multilayer wiring structure, it is necessary to etch the SiNx layer and to form at the SiNx layer a connecting hole such as a via hole through which the Cu wiring layer is exposed. However, a CF (fluorocarbon) processing gas containing O2 is usually utilized in the plasma etching process during which the SiNx layer is etched. As a result, the surface of the exposed Cu wiring layer becomes oxidized by O2 or an oxide compound is formed at the Cu wiring layer during the etching process. Such a reaction product raises the electrical resistance value at the area where the Cu wiring is connected with the other wiring, thereby presenting a problem in that the device characteristics of the semiconductor device are compromised.
An object of the present invention, which has been completed by addressing the problem of the prior art discussed above, is to provide a new and improved etching method and a new and improved plasma processing method that solve the problem above and other problems.
In order to achieve the object described above, in a first aspect of the present invention, an etching method for etching an SiNx layer present on a Cu layer formed at a work piece placed in a processing chamber by raising to plasma a processing gas introduced into the processing chamber, which is characterized in that the processing gas contains a gas constituted of C, H and F and O2, is provided.
In the etching process implemented by using the gas constituted of C, H and F according to the present invention, the exposed surface of the Cu layer is not oxidized readily. In addition, this effect is sustained regardless of whether or not O2 is present. For this reason, even when a, wiring, for instance, is connected at the exposed surface of the Cu layer, the electrical resistance value at the connection area is not raised. Furthermore, by adding O2 into the gas constituted of C, H and F, it becomes possible to even more effectively prevent the oxidation of the Cu layer.
The gas constituted of C, H and F should be CH2F2, CH3F or CHF3.
In addition, it is desirable to add an inert gas into the processing gas. When an inert gas is added into the processing gas, the contents of the gas constituted of C, H and F and O2 can be adjusted as necessary in correspondence to specific process requirements while maintaining the quantity of the processing gas introduced into the processing chamber at a predetermined level.
Moreover, in a second aspect of the present invention, a plasma processing method comprising a step in which an SiNx layer is etched by using a photoresist layer having a specific pattern formed therein, a step implemented after the etching step, a step implemented after said etching step, in which said photoresist layer is ashed and a step implemented after said ashing step, in which a plasma process is implemented on the exposed Cu layer by raising to plasma H2 introduced into the processing chamber is provided.
It is to be noted that the exposed surface of the Cu layer may become oxidized during the ashing step as well. In addition, if a CF gas is used as the processing gas during the etching step, C (carbon atoms) and F (fluorine atoms) may be injected into the exposed surface of the Cu layer. Accordingly, in a third aspect of the present invention, the surface of the Cu layer is treated with H2 plasma after the etching step and the ashing step to deoxidize the oxidized Cu and to remove C and F. As a result, the electrical resistance value at the connection area where the Cu wiring is connected to the other wiring is prevented from increasing even more effectively.